For certain types of patient care, air support patient beds have been in use for a considerable period of time. For example, during skin grafting procedures and for control of decubitus ulcers, also known as pressure lesions or bedsores and the like, air support beds have been found to provide considerable patient benefit. Beds of this character, however, have a number of significant drawbacks which, in many cases, have given hospitals, rest homes and other facilities cause for concern. For example, in many cases for patient comfort and safety, it is absolutely necessary that the air sac or air cell patient support devices remain inflated at all times. In most cases, it is quite necessary that the air sacs remain inflated within a preset pressure range to provide sufficient patient/air sac contact for even distribution of forces to the patient such that forces against any part of the patient's body remain sufficiently low that pressure lesions are unlikely.
In the event the air pressure in the air sacs of an air support bed is too low, the fabric material forming the air sacs tends to wrap around the patient to an excessive extent, thus preventing ambient air form reaching a good portion of the patient's body. In this case, there is a significant tendency for the patient to perspire heavily in areas where this wrap-around effect occurs. Continuous excessive perspiration can maintain excessive moisture present at the patient's skin for extended periods of time, thus adversely affecting the comfort and eventual recovery of the patient. This wrap-around effect also tends to force the shoulders of the patient toward one another, developing a condition which can be quite uncomfortable to the patient and causes spinal trauma. Obviously, the greater the contact between the patient and the material of the air sacs, the lower the mechanical pressure between the air sac material and the contact body surface area of the patient. Though softer air sacs effectively retard the development of pressure lesions, there is an optimum pressure range for each patient which establishes a balance between protection from pressure lesions and retarding excessive perspiration.
In present air support convalescent beds, particular preset pressures are established for air distribution lines and these preset pressures are maintained by adjustable control valves at the inlet, outlet or both the inlet and outlet sections of the air sac groups. In the event an air supply line to one of the groups of air sacs should become kinked or pinched by equipment located near the convalescent bed, obviously, the preset pressure within its particular group of air sacs will be improper. Moreover, there is no efficient procedure for detecting improper pressure settings in given air sac groups except upon visual inspection by nursing personnel. A condition of improper inflation can exist for an extended period of time, doing significant harm to the patient. The present invention also addresses this particular area of importance.
Another drawback of conventional air support bed systems arises in the event of emergency conditions, such as cardiac arrest for example. In the event of cardiac arrest, it is frequently necessary for nursing personnel to conduct cardiac pulmonary resuscitation (CPR) activities. These activities cannot be conducted efficiently on soft platforms as are typically provided by air support convalescent beds. In this case, the patient must sometimes be moved rapidly to the floor or to a stable platform to enable CPR activities to be conducted. The additional trauma caused by rapid patient transfer is detrimental to the safety and health of the patient. presently available air support bed systems are quite slow to render to a stable platform condition. In one such system, the blower must be deenergized and the air supply hose removed from the air supply manifold before the air sacs can be rapidly deflated. It is desirable, therefore, to provide an air support convalescent bed system which can be selectively controlled by nursing personnel to rapidly deflate the air sacs and provide a stable platform for the patient without necessitating removal of the patient from the convalescent bed and thereby minimizing trauma to the patient.
For years, air support surfaces have been utilized to help prevent the formation of decubitus ulcers. Various strategies have been formulated by a number of companies to achieve this end. To date, the various efforts can be characterized as either air fluidized support or low air loss support surfaces. Although the present invention is directed to the low air loss support surface category, it is prudent to point out that both technologies have as their primary aim the reduction of interface pressure (between patient and support surface) by maximizing the surface area that the support surface presents to its load (the patient).
All low air loss support surfaces are similar in design. All commercially available air support beds have air sacs or air cells that number form 15 to 30 for beds of normal length, that are connected by one method or another to a common air supply such as a constant speed compressor.
Since humans differ in height, weight, age and sex, there is a corresponding difference in mass distribution that must be taken into consideration when an individual is placed on one of these support surfaces. Obviously, if a constant speed compressor is employed as an air source, then some method of limiting or enhancing air flow to various areas or sections of the support surface to accommodate low mass, or high mass body parts is needed. The typical low air loss support surface found in clinical use today consists of approximately 20 air sacs, organized into, usually, five or so groups of four to five air sacs each. Each group is assigned the task of supporting the weight of a particular body section, i. e. head, trunk, pelvic section, legs, foot section, etc. Each air sac or group of air sacs receives air from the common air source via a distribution manifold with associated in line flow control valves (one for each group of air sacs) as is evident from FIG. 1.
As can be seen from illustration 1, in one example of the prior art, the air flow to various air sac groups can be adjusted to accommodate the various mass distribution, hence weight distribution of different human patients. As the name "low air loss support surface" implies, there is a continuous flow of air crossing the air sacs through either microscopic or macroscopic openings. The inline valves are therefore adjusted to present the optimum surface area to the load (patient).
Although one present day manufacturer has made an effort to control or regulate the set pressure to an extent, its effort is only effective against a rapid rise in pressure of an air sac group, such as when a patient rolls over and sinks an elbow into a particular air sac, thereby suddenly reducing its volume and consequently increasing its pressure. This is accomplished by means of a differential pressure regulator. A differential pressure regulator will not provide appropriate pressure adjustment for the situation in which pressure is reduced rather than increased, such as when air filters become clogged or an air supply hose becomes crimped or deformed to such extent that the air supply to a group of air sacs is diminished below the volume that is required. A differential pressure regulator also fails to accommodate the situation in which the air pressure in a particular air sac group is raised in near infinitesimal increments. Virtually all of the present day manufacturers of air support beds have no means for keeping the set pressures constant.
All of the air support surface systems discussed above represent examples of an open loop regulation system in which the effects of regulation are local and minimal and cannot control the performance of the entire system. This is, in effect, nothing more than overpressure regulation via "poppit" valves as set forth in FIG. 2 also representative of the prior art.
Preset pressure must then be defined. A procedure must also be established for presetting the pressures in each of the air sac groups to present optimum surface area to the load. No current manufacturer of low loss air support beds has a sound methodology for the correct or even acceptable setting of pressures within each of the air sac groups.
It is therefore a principle purpose of the present invention to provide a novel air support surface system together with a novel methodology for the automatic setting of pressure in each air sac and/or air sac group so that each air sac and/or air sac group presents optimal or near optimal surface area to the load (patient) and to maintain this preset pressure once achieved by means of a closed loop pressure regulation system such that overpressure or underpressure deviations from the optimum are automatically corrected.